1. Field of the Invention
The present invention relates to coatings for combustible building materials, and particularly roofing materials such as wooden shakes, to provide protection from ignition and the spread of combustion from external causes.
2. History of the Prior Art
Cedar shakes have found extensive use as roofing materials for housing and commercial buildings. Roofs fabricated from wooden shakes have an aesthetic appeal which with their effectiveness are attested by their extensive use for over a hundred years.
In comparison to some roofing materials which are noncombustible, such as those formed from ceramic tiles of various configurations, wooden shake roofs offer economic advantages as the roofing materials are of lower cost and their lower weight allows lower cost substructures which support the roofing materials. These economic advantages apply to new structures and to the re-roofing of existing structures.
An example of current shake roof construction practice might employ 24 inch long cedar shakes in widths of about 4 to 10 inches as applied to a roof substructure with a pitch of a 4 inch rise for a 12 inch horizontal run. Each horizontal row, or course, of shakes is secured to the substructure with nails or staples. A nominal 1/2 inch space is left between the shakes of an individual course, and these spaces between shakes are off-set 1/2 inches or more between adjacent courses. A roll of about 15 to 30 pound weight per 100 square feet of roofing felt of 18 inch width is applied over the top 4 inches of the shake course and secured to the substructure. A second course of shakes is applied and secured to the substructure so that a maximum of 10 inches of the bottom of the preceding shake course is exposed. This process is repeated to form the roof. Modifications of this generalized method are employed at the eaves, hips, ridges and valleys of roofs; as well as for the covering wall surfaces.
While durable, cedar shake roofs eventually lose their effectiveness as a water barrier after many years of exposure. This loss of effectiveness with time varies widely as it can be due to a number of factors and combinations of factors. These factors include substantial erosion of the exposed surfaces, alternate swelling and contraction of the shakes due to natural wetting and drying, sunlight degradation, degradation due to atmosphere heating and oxidation, water elutriation and vaporization of natural protective components of the wood shakes and biological degradation due to mildew and other organisms. These factors may manifest themselves by splitting, warping, and greater water absorbency of the wooden shakes with an attendant loss of mechanical integrity. The roofing felt, an asphalt impregnated organic felt may become embrittled because of some of these factors and hence become more susceptible to physical degradation.
Both the shakes and the roofing felt can be physically further damaged by wind induced movement, impact by air borne objects, and by human and animal traffic on the roof.
A particular hazard of cedar shake roofs is their susceptibility to combustion. This susceptibility is heightened during periods of low atmospheric humidity and high ambient roof temperatures caused by high atmospheric air temperatures and roof heating by incident sunlight. Exposure to such atmospheric conditions reduces the water content of the shakes and makes them more prone to ignition by electrical sparks from damaged electrical power lines, lightning, and various flying burning or high temperature objects. On ignition of the roofs at local points, the spread of fire is exacerbated by winds which can cause large roof sections and even entire building roofs to be engulfed in flame in a matter of minutes. Such conflagrations, particularly where several buildings are involved, are often beyond the capabilities of fire fighting organizations which may be available.
All of these naturally occurring climatic conditions can be present during the Santa Ana winds of coastal southern California. During these periods, winds of very low humidity, such as 15% relative humidity or less, arise from the interior deserts and may prevail for several days. Public records over more than twenty years have directly linked the climatic conditions of Santa Ana winds and the use of cedar shake roofs to extensive damage and destruction by fire.
A number of products have been marketed for application to existing shake roofs with the objective of reducing the susceptibility of such roofs to extensive damage by fire.
These products have had limitations in the following areas: (1) limited effectiveness; (2) lack of performance; (3) uniformity of application; and (4) the incorporation of materials in the coating formulations which require special handling considerations.
Examples of such products which have been marketed are Flame X Shingle Safe of the Flame X Control Corp. which contains mineral spirits which is a flammable hydrocarbon, and Fire Safe AD 108 of the Am Dal Chemical Corporation. Both of these suppliers claim that their products function by absorption on application by the roof materials. A reapplication of these products to roofs is recommended by the manufacturers after five to seven years for Flame X Shingle Safe and after five years for Fire Safe AD 108. Neither manufacturer claims that their product on application significantly adds to the mechanical integrity of the exterior roof surface or would improve the roof ability to shield the interior building from water penetrating the roof.
Accordingly, it is an objective of this invention to provide an extensible dried exterior coating that enhances the mechanical integrity, life, and water sealing capabilities of the roof by virtue of the adherent properties of the coating and the mechanical and water sealing properties of the dried coating.
It is a further object of this invention to provide a water based coating composition for roofs which greatly increases the resistance of the roof from exterior ignition and spreading conflagration without requiring a substantial penetration of the coating into the wood.
It is a still further objective of this invention to provide a low cost, fire resistant roof dried coating material which on local exposure to a temperature of 1000.degree. C. leaves an inert residue of 50 percent by weight or more after an exposure of several minutes.